During approximately the last decade, short strips, or tabs, of normally tacky and pressure-sensitive adhesive tape have replaced safety pins as the means for closing disposable diapers. Prior to the present invention, each known tape had its own unique advantages and disadvantages, no such tape proving completely satisfactory.
Heretofore, the most widely used tape for diaper closures comprised a paper backing treated with a moisture-resistant polymer, provided on one face with a normally tacky and pressure-sensitive adhesive and on the other face with a release coating. Paper is a surprisingly expensive material, and its cost is increased by the several treatments to which it is subjected in preparing a tape suitable for diaper closure use. Even treated paper retains a moisture-sensitivity which occasionally weakens it sufficiently to cause it to fail when used as the backing in a tape closure for a diaper worn by an active baby. Further, paper is comparatively stiff, so that the edge of a paper tape closure may injure a baby's tender skin. An additional problem arises if the edge of the closure is inadvertently nicked, as may occur during the process of cutting tabs from a roll of tape prior to attaching them to diapers. It has been found that when such an edge-nicked tab is subjected to twisting tensile forces by an active infant, a tear often propagates across the tab, commencing at the weakened nicked edge.
Cloth is more attractive, flexible and tear-resistant than paper, but the process of weaving it is expensive, special treatments are required to prevent the penetration of adhesive when it is used as a tape backing, and there is a tendency for it to ravel. Various types of non-woven backings, including the so-called "spun-bonded" polymeric backings, are less expensive to make and more ravel-resistant than cloth, but their thickness, tear-resistance, etc. are not uniform; further, their open nature makes it both difficult and expensive to apply an adhesive coat.
For many years, various polymeric foils have been employed as the backings for normally tacky and pressure-sensitive adhesive tape. Some such tape has been suggested for use in connection with diapers; see, e.g., U.S. Pat. Nos. 2,002,368, 3,630,201 and 3,937,221. Although polymeric foils may be comparatively inexpensive, when conventional foil-backed tape is used as a diaper closure, it displays one or more of such disadvantages as excessive stiffness (which increases the difficulty of preparing closure strips and causes discomfort to the wearer), or poor resistance to tearing across the closure when subjected to tensile stress along the length of the closure, especially if one edge is inadvertently nicked.
Disposable diapers have a moisture-permeable inner foil liner which contacts the baby, a moisture-absorbent central fluff layer, and a moisture-impermeable outer foil cover (usually polyethylene). A tape closure is typically adhered to the cover on both of two juxtaposed or overlapping diaper portions. Such closures adhere strongly to the foil and thus generally cannot be pulled loose without tearing the cover; while closures are often opened in this way, the central layer is thereby exposed, permitting the inner fluff to fall out. An alternative way to open the closure is to cut or tear it across its length. Since heretofore a closure which could be easily torn when the diaper was removed might inadvertently be prematurely torn by an active diapered baby, it has often been preferred to have a closure which could be cut with a scissors but not readily torn. On the other hand, when a scissors is not available, and the closure cannot be torn, the diaper cover is frequently ripped open, with the undesirable results previously mentioned.